This invention relates in general to furnaces and more particularly to a furnace and process for melting metals so as to provide a source of molten metal.
Aluminum and its alloys melt at relatively low temperatures, and this coupled with other desirable characteristics, render aluminum ideal for casting and extruding operations. It is quite common to derive the molten aluminum for these operations from a furnace into which both aluminum ingots or sows and aluminum scrap are introduced. The sows, however, require special precautions in handling, because they may, if introduced into a bath of molten aluminum produce an explosion. In this regard, the typical cast aluminum sow often contains shrinkage cracks in which water collects, and this water if suddenly elevated in temperature, such as might occur if the sow were deposited into the bath of molten aluminum, could well produce an explosion of sufficient magnitude to destroy the furnace.
For this reason it is common to slowly preheat aluminum sows so a to vaporize the water and drive it off before the sows are introduced into the molten aluminum. Such preheating may take place within the melting furnace itself or in a separate preheating furnace.
In this regard, the typical aluminum furnace has a sill located to the side of the molten aluminum bath and exposed in its entirety to the heated chamber over the bath. This chamber is heated by burners which are directed into it, and these burners supply enough heat to melt the aluminum and maintain it in a molten condition. The sows to the side of the bath absorb much heat from the chamber, both through the effects of radiation and convection, and indeed the latter is enhanced by venting the chamber through the region in which the sows are located, so that the heated gases flow across the sows as they leave the chamber. In time the sows melt and molten aluminum which is produced flows into the bath, thus adding to the bath.
The presence of a large number of sows in the chamber enables the sows to absorb heat which might otherwise be directed into the aluminum bath to maintain the aluminum of that bath molten. In other words, the walls of the melting chamber, instead of radiating heat almost entirely into the bath, radiate a substantial amount of heat to the sows. This wastes energy in that the chamber must be overheated to effect a melting of the sows.